A shipping carrier is a company that provides shipping services for letters, packages, bulk goods, or any other item to be shipped. Carriers can perform a variety of shipping services. For example, they can deliver express shipments, e.g. airmail for letters and second-day air for small packages. Moreover, carriers can deliver ground shipments for packages, or "LTL" shipments for bulk goods. The term "LTL" means "Less Than Truckload" and applies to any ground carrier shipment of standard commodities, for example, rated in units of hundreds of pounds. Shipments of bulk goods or standard commodities usually occupy a portion of a truck trailer, hence "less than truckload," but may require an entire truckload, occasionally known as "TL" shipments.
Each carrier has its own rate structure for charging shippers for transporting their goods. Typically, these rates structures are complex and involve a variety of factors. For example, carriers often charge different prices by weight, sometimes with different weight classifications. As another example, carrier rates may be dependent on the distance to the destination. In addition, some carriers charge a premium for shipping classes, e.g. first class and second class, with shorter or longer guaranteed delivery times. In some cases, carriers may grant discounts for volume. Thus, the business rules for rating items to be transported varies greatly from carrier to carrier. These rating calculations may change over time for a particular carrier as its rates and business rules are updated. Accordingly, it is desirable to provide mechanisms for logistics systems for shipping goods to facilitate updating how carrier rates are calculated.
According to one approach, the carrier rate information and business rules are isolated into separately executable programs on a per-carrier basis. Thus, updating a carrier rating program can occur independently of other carrier rating programs. For example, U.S. Pat. No. 5,631,827 issued May 20, 1997 to Nicholls et al. describes a logistics system in which carrier rate information and business rules are isolated into separate program objects, called "rate servers." These rate servers are spawned by a client process or a supervisory manager process and are concurrently executed with the client and supervisory processes in a multitasking operating system. Consequently, the rate servers communicate with the client and supervisory manager processes via an interprocess communication (IPC) mechanism, such as a named pipe. In this system, a client program formulates a tokenized message with information about an item to be rated and passes the tokenized message to a rate server for a desired carrier via a named pipe. The operating system suspends execution of the client program and performs a context swap granting the rate server a time slice to compute the rate calculation. When activated, the rate server decodes the tokenized message, performs the rate calculation, tokenizes a response, and sends the tokenized response back to the client program through IPC. Finally, the operation system puts the rate server to sleep and executes another context swap to resume execution of the client program, which decodes the tokenized response.
This system is resource intensive. For example, each concurrently executing rate server takes up an entry in a process table of the operating system, reducing the number of other processes that may be run concurrently. Moreover, there is processing overhead in tokenizing and decoding the messages used for the IPC mechanism as well as the overhead involved in the IPC mechanism itself. Another reason why the described system is resource intensive is that two context swaps are performed for every rate calculation. Context swaps are generally expensive in terms of processing time, because, for example, processor registers have to be saved and restored.
Often, it is difficult to add support for new carriers to conventional logistic systems. For example, the system described by Nicholls et al. employs a supervisory server for managing one or more carriers, and corresponding rate server and rate administrator programs for handling tasks specific to a carrier. As disclosed in TABLE II of the Nicholls et al. reference, the supervisory server associates each carrier with a program identifier from a file called PROGISTI.H. The ".H" suffix of the file conventionally indicates a header file, which are used to hard-code the program identifiers at compile time into the supervisory server executable. Thus, to add support for a new carrier in such a system, the source code and header files for at least the supervisory server have to be modified. A new supervisory server executable program object must be compiled, distributed to the customer's site, and re-installed, often at a substantial monetary cost.